1. Field of the Invention
The present invention relates to a wireless local access network (WLAN), and more particularly, to a data transmission method in a wireless mesh network and a format of an aggregate-medium access control service data unit (A-MSDU) used in the data transmission method.
2. Description of the Related Art
With the recent development of information communication technology, a variety of wireless communication technology has been developed. A WLAN is the technology permitting wireless access to Internet in home or companies or specific service areas by the use of portable terminals such as a personal digital assistant (PDA), a laptop computer, and a portable multimedia player (PMP) on the basis of a radio frequency technology.
The IEEE (Institute of Electrical and Electronics Engineers) 802 which is a standardization of the WLAN technology established in February, 1980 has carried out much standardization work. In the initial WLAN technology, a data rate of 1 to 2 Mbps was supported by the use of frequency hopping, spread spectrum, and infrared communication using a frequency of 2.4 GHz in accordance with the IEEE 802.11. In recent years, 54 Mbps in maximum can be supported by the use of the orthogonal frequency division multiplex (OFDM) technology to the WLAN. In addition, the IEEE 802.11 has developed or is developing a variety of technical standards for improvement in quality of service (QoS), compatibility of an access point (AP) protocol, security enhancement, wireless resource measurement, wireless access in vehicular environment, fast roaming, wireless mesh network, inter-working with external networks, wireless network management, and the like.
The “wireless mesh network” can support direct communication between plural wireless stations having a relay function. In view of functionality, a distribution system (DS) for plural APs can be replaced with an inter-operable wireless link or a multi-hop path between the plural wireless stations. In the mesh network, one wireless station can set up a peer-to-peer wireless link with one or more neighboring wireless stations, thereby constructing a more flexible network.
In the wireless mesh network, one wireless station can establish plural peer links with each of other wireless stations. Thus, plural communication paths can exist between two wireless stations. Among them, the direct communication paths between two wireless stations are called a wireless mesh link or a mesh peer link or a peer link. The wireless stations are called mesh points (MP), which is only an example. A wireless station performing the function of an AP is called mesh access point (MAP).
Such a wireless mesh network has advantages such as flexibility in constructing a network, reliability due to bypass paths, reduction in power consumption due to a decrease in communication distance. More specifically, it is possible to construct a flexible network by using the mesh network even in places not including any wired communication network. In the mesh network, the plural MPs can be connected to each other to guarantee plural bypass paths. Accordingly, even when one MP is out of order, data can be transmitted through another path. In the mesh network, since the communication can be made through a neighboring MP, it is possible for terminals to communicate with low power.
On the other hand, the IEEE 802.11n defines a frame aggregation. The frame aggregation is a protocol for aggregating plural frames (for example, data frames or management action frames) and then transmitting the aggregated frames at one time, or transmitting the aggregated frames in several fragments. In the frame aggregation, an aggregate-MAC service data unit (A-MSDU) is a new format of data acquired by aggregating plural MSDUs. One A-MSDU may be inserted into one MAC protocol data unit (MPDU) and may be then transmitted, or may be divided and inserted into plural MPDUs and may be then transmitted. The plural MSDUs constituting one A-MSDU have the same traffic identifier (TID).
FIG. 1 is a diagram illustrating a format of an A-MSDU described in the IEEE 802.11n standard.
Referring to FIG. 1, the A-MSDU includes plural A-MSDU sub-frames. That is, the basic unit of the A-MSDU is an A-MSDU sub-frame. Each A-MSDU sub-frame includes a sub-frame head field, a MSDU field, and a padding field. The padding field exists in all the A-MSDU sub-frames except for the final A-MSDU sub-frame and is an additional field allowing the length of the A-MSDU sub-frame to be a multiple of 4 octets.
The sub-frame header field includes three subfields. That is, the sub-frame header field includes a destination address subfield (DA), a source address subfield (SA), and a length subfield. The destination address subfield (DA) may be set to the MAC address of a wireless station as the final destination of the A-MSDU sub-frame. The source address subfield (SA) may be set to the MAC address of a wireless station first having initiated the transmission of the A-MSDU sub-frame. The length subfield may be set to a value indicating the length of the MSDU field in the unit of octet.